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There are comments that you should not adjust the gap sizes of the plugs and use them the way they come out of the box. Hmmm .. I have a 1999 Grand Prix GTP with the 3.8L V6 supercharged engine. My GM owners manual states a gap of .060 for all the replacement plugs listed not only for my engine but for all Grand Prix engine sizes of that year 3.1 / 3.8 / 3.8SC Check your GM owners manual .. it will state there in the section of different replacement parts, what spark plugs to use and the gap size

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Q: What is the spark plug gap on a 99 grand prix 3.8 liter?
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